1. Field of the Invention
The present invention relates generally to amplifier systems having bias signals provided by bias generators.
2. Description of the Related Art
A significant number of bias generators have been proposed for providing bias signals that enhance and/or stabilize transistor amplifier parameters (e.g., amplifier current, transconductance, voltage gain, and noise) in the presence of process, voltage supply and temperature (PVT) variations.
These generators have generally failed to effectively control at least one contributing source of error in amplifier performance. For example, several of these bias generators are configured so that an important metal-oxide-semiconductor (MOS) bias transistor has a body-to-source voltage VBS that differs from others of the bias transistors. This causes at least one bias transistor to exhibit a “body effect” which alters its threshold voltage VTH so that its drain current is no longer a reliable function of its gate-to-source voltage VGS. Accordingly, significant errors are introduced into transistor parameters (e.g., transconductance).
In order to reduce these body-effect errors, some bias generators have emphasized the use of P-type transistors which can typically have their transistor bodies (i.e., wells) coupled to their sources. This, however, generally requires an associated amplifier of the system to also use P-type transistors which typically reduces the system's maximum operating frequency.
Conventional bias generators have also generally:    a) introduced bias errors by failing to address errors introduced by the Early effect,    b) failed to address the stabilization of transistor transconductances in systems that include a mix of P-type and N-type transistors,    c) ignored system noise performance with the result that it is often degraded, and/or    d) eliminated other problems at the cost of increased system size and/or system power consumption.